Neurons that produce histamine are exclusively located in the tuberomamillary nucleus of the posterior hypothalamus and send widespread projections to almost all brain areas. Neuronal histamine is ... [more ▼]

Neurons that produce histamine are exclusively located in the tuberomamillary nucleus of the posterior hypothalamus and send widespread projections to almost all brain areas. Neuronal histamine is involved in many physiological and behavioral functions such as arousal, feeding behavior and learning. Although conflicting data have been published, several studies have also demonstrated a role of histamine in the psychomotor and rewarding effects of addictive drugs. Pharmacological and brain lesion experiments initially led to the proposition that the histaminergic system exerts an inhibitory influence on drug reward processes, opposed to that of the dopaminergic system. The purpose of this review is to summarize the relevant literature on this topic and to discuss whether the inhibitory function of histamine on drug reward is supported by current evidence from published results. Research conducted during the past decade demonstrated that the ability of many antihistaminic drugs to potentiate addictionrelated behaviors essentially results from non-specific effects and does not constitute a valid argument in support of an inhibitory function of histamine on reward processes. The reviewed findings also indicate that histamine can either stimulate or inhibit the dopamine mesolimbic system through distinct neuronal mechanisms involving different histamine receptors. Finally, the hypothesis that the histaminergic system plays an inhibitory role on drug reward appears to be essentially supported by place conditioning studies that focused on morphine reward. The present review suggests that the development of drugs capable of activating the histaminergic system may offer promising therapeutic tools for the treatment of opioid dependence. [less ▲]

RATIONALE: Previous studies have shown that intraperitoneal injections of thioperamide, an imidazole-based H(3) receptor inverse agonist that enhances histamine release in the brain, potentiate cocaine-induced hyperlocomotion. The present study examined the involvement of the histaminergic system in these effects of thioperamide in mice. MATERIALS AND METHODS: We investigated whether immepip, a selective H(3) agonist, could reverse the potentiating effects of thioperamide. Moreover, the non-imidazole H(3) inverse agonist A-331440 was tested on the locomotor effects of cocaine. Using high-performance liquid chromatography with ultraviolet detection, cocaine plasma concentrations were measured to study potential drug-drug interactions between thioperamide and cocaine. Finally, thioperamide was tested on the locomotor effects of cocaine in histamine-deficient knockout mice in order to determine the contribution of histamine to the modulating effects of thioperamide. RESULTS: Thioperamide potentiated cocaine-induced hyperlocomotion in normal mice, and to a higher extent, in histamine-deficient knockout mice. A-331440 only slightly affected the locomotor effects of cocaine. Immepip did not alter cocaine-induced hyperactivity but significantly reduced the potentiating actions of thioperamide on cocaine's effects. Finally, plasma cocaine concentrations were more elevated in mice treated with thioperamide than in mice that received cocaine alone. CONCLUSIONS: The present results indicate that histamine released by thioperamide through the blockade of H(3) autoreceptors is not involved in the ability of this compound to potentiate cocaine induced-hyperactivity. Our data suggest that thioperamide, at least at 10 mg/kg, increases cocaine-induced locomotion through the combination of pharmacokinetic effects and the blockade of H(3) receptors located on non-histaminergic neurons. [less ▲]

So far, small conductance Ca2+-activated K+ channel (SK) blockers mostly consist of quaternary ammonium derivatives or peptides. Due to their physicochemical properties, these blockers are not suitable to ... [more ▼]

So far, small conductance Ca2+-activated K+ channel (SK) blockers mostly consist of quaternary ammonium derivatives or peptides. Due to their physicochemical properties, these blockers are not suitable to study the physiological roles of SK channels in the central nervous system in vivo. Herein, we report the discovery of a chiral bis-tertiary amine with SK blocking properties from chemical modulation of laudanosine. AG525E1 has an affinity for SK channels (K-i = 293 nM) approximately 100-fold higher than the tertiary compound laudanosine (K-i similar to 30 mu M) and similar to the charged compound dequalinium (K-i = 221 nM). AG525E1 equipotently blocks SK1, SK2 and SK3 currents in transfected cell lines. Because of its basic and lipophilic properties, it can reach central SK targets. (c) 2008 Elsevier Ltd. All rights reserved. [less ▲]

Several methoxylated 1,2,3,4-tetrahydroisoquinoliniums derived from N-methyl-laudanosine and N-methyl-noscapine were synthesized and evaluated for their affinity for apamin-sensitive binding sites. The ... [more ▼]

Several methoxylated 1,2,3,4-tetrahydroisoquinoliniums derived from N-methyl-laudanosine and N-methyl-noscapine were synthesized and evaluated for their affinity for apamin-sensitive binding sites. The quaternary ammonium derivatives have a higher affinity with regard to the tertiary amines. 6,7-Dimethoxy analogues possess a higher affinity than the 6,8- and 7,8- dimethoxy isomers. A 3,4-dimethoxybenzyl or a 2-naphthylmethyl moiety in C-1 position are more favorable than a 3,4-dimethoxyphenethyl group. Smaller groups such as propyl or isobutyl are unfavorable. In 6,7-dimethoxy analogues, increasing the size and lipophilicity with a naphthyl group in the C-1 position leads to a slight increase of affinity, while the same group in the 6,7,8- trimethoxy series is less favorable. The 6,7,8- trimethoxy derivative 3f is the first tertiary amine in the series to possess an affinity close to that of N-methyl-laudanosine and N-methyl-noscapine. Moreover, electrophysiological studies show that the most effective compound 4f blocks the apamin-sensitive afterhyperpolarization in rat dopaminergic neurons. [less ▲]

K channels are small conductance calcium-activated potassium channels which trigger an outward current generating an afterhyperpolarization (AHP). This AHP follows a single or a train of action potential ... [more ▼]

K channels are small conductance calcium-activated potassium channels which trigger an outward current generating an afterhyperpolarization (AHP). This AHP follows a single or a train of action potential, and therefore is important in the regulation of the firing frequency and/or pattern of many types of neurons. Serotonergic (5-HT) neurons from the raphe nuclei express SK channels and exhibit a significant AHP which can be efficiently blocked in vitro by apamin and N-methyl laudanosine (NML) (Scuvée-Moreau et al, 2004). In the later study, we found that some but not all neurons (50%) had a significantly increase in their firing rate when positive current was injected after SK channel blockade. In order to determine the physiological relevance of these channels in vivo, single unit extracellular recordings were carried out in anesthetized rats and combined with iontophoresis of the specific non-peptidic SK channel blocker, UCL1684. 5-HT neurons were tested for their inhibitory response to locally applied 5-HT and histological analysis confirmed the localization of the recording site. UCL 1684 was used at a concentration of 200 µM. Out of 11 neurons recorded, 6 showed a significant increase in the production of doublets, with no effect on their mean firing rate as compared to the control condition. The other neurons were completely unaffected. These results suggest that the responsiveness of presumed 5-HT neurons to SK channel block is variable. Although the use of 200 µM UCL allow us to be sure of a sufficient SK blockade at the recording site (Waroux et al, 2005), we can not rule out the possibility that SK channels present at the dendritic level were not completely blocked. In conclusion, SK channels in vivo might play a role in controlling the firing pattern of a subgroup of 5-HT neurons. [less ▲]

A vast body of experimental in vitro work and modelling studies suggests that the firing pattern and/or rate of a majority of midbrain dopaminergic neurons may be controlled in part by Ca2+-activated K ... [more ▼]

A vast body of experimental in vitro work and modelling studies suggests that the firing pattern and/or rate of a majority of midbrain dopaminergic neurons may be controlled in part by Ca2+-activated K+ channels of the SK type. However, due to the lack of suitable tools, in vivo evidence is lacking. We have taken advantage of the development of the water-soluble, medium potency SK blocker N-methyl-laudanosine (CH3-L) to test this hypothesis in anaesthetized rats. In the lateral ventral tegmental area, CH3-L iontophoresis onto dopaminergic neurons significantly increased the coefficient of variation of their interspike intervals and the percentage of spikes generated in bursts as compared to the control condition. The effect of CH3-L persisted in the presence of a specific GABA(A) antagonist, suggesting a direct effect. It was robust and reversible, and was also observed in the substantia nigra. Control experiments demonstrated that the effect of CH3-L could be entirely ascribed to its blockade of SK channels. On the other hand, the firing pattern of noradrenergic neurons was much less affected by CH3-L. We provide here the first demonstration of a major role of SK channels in the control of the switch between tonic and burst firing of dopaminergic neurons in physiological conditions. This study also suggests a new strategy to develop modulators of the dopaminergic (DA) system, which could be of interest in the treatment of Parkinson's disease, and perhaps other diseases in which DA pathways are dysfunctional. [less ▲]